CN107407183B

CN107407183B - Exhaust gas purification unit

Info

Publication number: CN107407183B
Application number: CN201680019151.9A
Authority: CN
Inventors: 大原功; 长田胜士
Original assignee: Isuzu Motors Ltd
Current assignee: Isuzu Motors Ltd
Priority date: 2015-03-30
Filing date: 2016-03-29
Publication date: 2020-06-23
Anticipated expiration: 2036-03-29
Also published as: US20180112571A1; EP3279440A4; WO2016158993A1; EP3279440B1; CN107407183A; US11149611B2; EP3279440A1

Abstract

The method comprises the following steps: a connection pipe (24) that transports the exhaust gas into the SCR catalyst (41); a urea solution injection valve (30) that is disposed so as to face the exhaust upstream end of the connection pipe (24) and injects urea solution into the connection pipe (24); a mixing chamber (23) that forms a flow path through which exhaust gas flows from the exhaust downstream end of the front-stage casing (20) to the exhaust upstream end of the connecting pipe (24) while turning back; and a flow regulating member (50) which is provided in the mixing chamber (23), is a truncated cone-shaped member extending from the vicinity of the injection port of the urea solution injection valve (30) toward the connection pipe (24) while gradually expanding in diameter, and has a plurality of small holes (50C), and a claw (50D) for guiding the exhaust gas to the exhaust downstream side is provided in each of the small holes (50C).

Description

Exhaust gas purification unit

Technical Field

The present invention relates to an exhaust gas purification unit including an SCR catalyst.

Background

As an exhaust gas purification unit that reductively purifies nitrogen oxides (NOx) in exhaust gas discharged from an internal combustion engine, there is known an exhaust gas purification unit including: a front stage including an oxidation catalyst or a filter that traps particulate matter (hereinafter, referred to as PM) in exhaust gas; and a rear stage unit including a selective reduction catalyst (hereinafter, referred to as an SCR catalyst) for purifying nitrogen oxides (hereinafter, referred to as NOx) in exhaust gas using ammonia generated from urea water as a reducing agent (see, for example, patent documents 1 and 2).

In the exhaust gas purification unit described in patent document 1, a front-stage casing that houses an oxidation catalyst and a filter is arranged in parallel with a rear-stage casing that houses an SCR catalyst, and an upstream end and a downstream end of a linear pipe arranged between the front-stage casing and the rear-stage casing are connected to an outlet of the front-stage casing and an inlet of the rear-stage casing, respectively. A urea water injection device is disposed at an upstream end of the pipe, and urea water is added to exhaust gas introduced from the front-stage casing to the rear-stage casing, whereby the urea water is hydrolyzed in the exhaust gas to generate ammonia, and the ammonia is supplied as a reducing agent to the SCR catalyst, whereby NOx in the exhaust gas is reductively purified.

In the exhaust gas purification unit described in patent document 2, a swirl flow generating vane for swirling exhaust gas is provided upstream of the urea water injection position, and the exhaust gas as a swirl flow and the injected urea water are mixed in a pipe.

Documents of the prior art

Patent document

Patent document 1 Japanese patent laid-open No. 2009-36109

Patent document 2 Japanese laid-open patent publication No. 2006-29233

Disclosure of Invention

Problems to be solved by the invention

The urea aqueous solution is injected from the vicinity of the upstream end of the pipe toward the downstream side, and the exhaust gas is introduced from the front stage casing to the upstream end of the pipe so as to intersect the flow of the exhaust gas. Therefore, a part of the injected urea water is flushed and adhered to the wall surface of the upstream portion of the pipe by the exhaust gas before being diffused. Therefore, the efficiency of hydrolysis of the urea water deteriorates, and the diffusivity of ammonia in the exhaust gas supplied to the SCR catalyst decreases, thereby reducing the exhaust gas purification ability of the SCR catalyst.

An object of the exhaust gas purification unit of the present disclosure is to improve the exhaust gas purification ability of a catalyst by improving the efficiency of urea water hydrolysis and improving the diffusivity of ammonia in exhaust gas.

Means for solving the problems

The exhaust gas purification unit of the present disclosure includes: a selective reduction catalyst that is provided in an exhaust system of an internal combustion engine and selectively reduces nitrogen oxides in exhaust gas using ammonia as a reducing agent, an exhaust pipe, a urea solution injection device which is disposed so as to face the exhaust upstream end of the exhaust pipe and injects urea solution into the exhaust pipe, an air supply chamber, which connects an exhaust downstream end of a housing containing a catalyst and an exhaust upstream end of the exhaust pipe, and a flow path for returning the exhaust gas from the casing to the exhaust pipe, and a flow regulating member, a plurality of air vents formed in a pipe member of a truncated cone shape extending from the vicinity of the injection port of the urea solution injection device toward the exhaust pipe while gradually expanding the diameter of the pipe member, each of the vents is provided with a guide portion for guiding the exhaust gas to the exhaust downstream side.

Further, the exhaust gas purification unit of the present disclosure includes: a selective reduction catalyst that is provided in an exhaust system of an internal combustion engine and selectively reduces nitrogen oxides in exhaust gas using ammonia as a reducing agent, an exhaust pipe that transports exhaust gas to the selective reduction catalyst, a urea water injection device that injects urea water into the exhaust pipe, and an exhaust gas introduction portion that is connected to the exhaust pipe and has a plurality of vents formed therein; the exhaust pipe includes an inner pipe through which the urea solution is injected from the urea solution injection device, and an outer pipe having a double pipe structure together with the inner pipe, and a flow path for exhaust gas is formed inside the inner pipe and between the inner pipe and the outer pipe; the exhaust gas introduction section is connected to the exhaust upstream end of the inner pipe, and is formed in a truncated cone shape so as to extend from the vicinity of the injection port of the urea solution injection device to the exhaust upstream end of the inner pipe while gradually expanding in diameter.

Effects of the invention

According to the exhaust gas purification unit of the present disclosure, the efficiency of urea water hydrolysis is improved, and the diffusivity of ammonia in the exhaust gas is improved, thereby making it possible to improve the exhaust gas purification capability of the catalyst.

Brief description of the drawings

Fig. 1 is a perspective view showing an exhaust gas purification unit according to an embodiment.

Fig. 2 is a cross-sectional view showing the interior of the mixing chamber and the connecting pipe.

Fig. 3 is a diagram showing the flow of the exhaust gas in the mixing chamber.

Fig. 4 is a diagram showing the flow of the exhaust gas in the mixing chamber.

Fig. 5 is a sectional view showing a rectifying unit according to another embodiment.

Fig. 6 is a sectional view showing a rectifying unit according to another embodiment.

Fig. 7 is a sectional view showing a rectifying unit according to another embodiment.

Fig. 8 is a sectional view showing a rectifying unit according to another embodiment.

FIG. 9 is a sectional view showing the inside of a mixing chamber and a connecting pipe according to another embodiment.

Fig. 10 is a diagram showing the flow of the exhaust gas in the mixing chamber and the connection pipe in another embodiment.

Detailed Description

Hereinafter, one embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a perspective view showing an exhaust gas purification unit 1 according to an embodiment. As shown in the drawing, the exhaust gas purification unit 1 includes, in order from the exhaust upstream side: forecasing 20, mixing chamber 23, urea water injection valve 30, connecting piping 24, and after casing 40.

The front stage casing 20 and the rear stage casing 40 are cylindrical, are arranged in parallel with their axes parallel to each other, and are connected by a connection pipe 24 disposed therebetween. The connection pipe 24 includes a cylindrical 1 st pipe 24A, and an axis of the pipe 24A is arranged parallel to axes of the front stage casing 20 and the rear stage casing 40.

The front stage casing 20 includes: the 1 st case 20A; and a 2 nd casing 20B coaxially disposed on the exhaust downstream side of the 1 st casing 20A. An annular flange is provided at the exhaust downstream end of the 1 st casing 20A and the exhaust upstream end of the 2 nd casing 20B, and both flanges are connected by bolts and nuts. Further, in the 1 st casing 20A, a 1 st oxidation catalyst 21 is housed, and in the 2 nd casing 20B, a filter 22 is housed.

The 1 st oxidation catalyst 21 is, for example, a catalyst in which a catalyst component or the like is supported on the surface of a ceramic support such as a cordierite honeycomb structure. The 1 st oxidation catalyst 21 oxidizes unburned Hydrocarbon (HC) supplied by the far after injection or the exhaust pipe injection to raise the exhaust gas temperature.

The filter 22 is, for example, a filter in which a plurality of cells partitioned by porous partition walls are arranged along the flow direction of the exhaust gas, and the upstream side and the downstream side of the cells are alternately closed. The filter 22 collects particulate matter (hereinafter, referred to as PM) in the exhaust gas in the pores or the surface of the partition wall, and burns and removes the PM when a predetermined amount of PM accumulation is estimated and so-called forced filter regeneration is performed. Here, the forced filter regeneration is performed by supplying unburned hydrocarbons to the 1 st oxidation catalyst 21 on the exhaust gas upstream side by exhaust pipe injection or after injection, and raising the temperature of the exhaust gas flowing into the filter 22 to the PM combustion temperature.

The mixing chamber 23 includes: a 1 st chamber 23A disposed at an exhaust downstream end of the 2 nd casing 20B and having an arc-shaped side surface; and a 2 nd chamber 23B extending from a side surface of the 1 st chamber 23A to the rear stage casing 40 side, the side surface being arc-shaped. The 1 st chamber 23A is configured to be coaxial with the 2 nd housing 20B. The diameter of the 2 nd chamber 23B is smaller than that of the 1 st chamber 23A, and the boundary between the two chambers is curved in an arc shape.

Annular flanges are provided at the exhaust downstream end of the 2 nd casing 20B and the exhaust upstream end of the 1 st chamber 23A, and the flanges are connected by bolts and nuts.

The connection pipe 24 includes: a cylindrical 1 st pipe 24A connected to the 2 nd chamber 23B; and a 2 nd pipe 24B connecting the 1 st pipe 24A and the exhaust upstream end of the rear stage casing 40. The 1 st pipe 24A is disposed coaxially with the injection axis of the urea solution injection valve 30.

The 2 nd pipe 24B is an elbow pipe, and the exhaust downstream end is formed into a disk shape. The straight portion of the 2 nd pipe 24B is arranged coaxially with the 1 st pipe 24A, and annular flanges are provided at the exhaust downstream end of the 1 st pipe 24A and the exhaust upstream end of the 2 nd pipe 24B, and both flanges are connected by bolts and nuts. Further, annular flanges are provided at the exhaust downstream end of the 2 nd pipe 24B and the exhaust upstream end of the rear stage casing 40, and the flanges are connected by bolts and nuts.

The urea solution injection valve 30 is provided in the 2 nd chamber 23B. The injection axis of the urea solution injection valve 30 is aligned with the axial center of the connection pipe 24, and urea solution is injected (sprayed) from the urea solution injection valve 30 to the exhaust downstream side of the connection pipe 24.

In the connection pipe 24, the urea water injected from the urea water injection valve 30 and the exhaust gas flowing from the mixing chamber 23 to the rear stage casing 40 are mixed, and the urea water is hydrolyzed by exhaust heat to generate ammonia (NH)₃). The generated ammonia is supplied to the SCR catalyst 41 on the exhaust downstream side by the flow of the exhaust gas.

The rear stage case 40 houses an SCR catalyst 41 and a 2 nd oxidation catalyst 42 disposed on the exhaust gas downstream side of the SCR catalyst 41.

The SCR catalyst 41 is, for example, a catalyst in which zeolite or the like is supported on a porous ceramic support. The SCR catalyst 41 adsorbs ammonia as a reducing agent supplied from the urea water injection valve 30, and selectively reduces and purifies NOx from the passing exhaust gas by the adsorbed ammonia.

The 2 nd oxidation catalyst 42 is a catalyst in which a catalyst component or the like is supported on the surface of a ceramic support such as a cordierite honeycomb structure, for example, and has a function of oxidizing ammonia that leaks from the SCR catalyst 41 to the exhaust gas downstream side.

Fig. 2 is a sectional view showing the interior of the mixing chamber 23 and the connecting pipe 24. As shown in the figure, a rectifying portion 51 is provided in the 2 nd chamber 23B of the mixing chamber 23, and a rectifying member 50 is provided in the rectifying portion 51. The flow straightening member 50 is a pipe member of a truncated cone shape having both ends open, and is disposed coaxially with the urea solution injection valve 30.

The small-diameter opening 50A of the flow regulating member 50 is disposed so as to face the injection port of the urea solution injection valve 30, and a part of the large-diameter opening 50B of the flow regulating member 50 is inserted into the upstream end of the connection pipe 24. A gap through which exhaust gas passes is provided between the outer peripheral surface of the edge of the opening 50B of the flow rectification member 50 and the inner peripheral surface of the upstream end of the connection pipe 24.

The flow straightening member 50 is a porous member, and rectangular small holes 50C are formed at narrow intervals in the circumferential direction and the axial direction. Here, the small hole 50C is formed by cut-and-bend processing, and the claw 50D is bent inward of the flow regulating member 50 with the upstream side of the small hole 50C as a starting point. The angle of the cut-and-raised bend of the claw 50D is an acute angle, and the claw 50D functions as a guide portion that guides the exhaust gas that has passed through the small hole 50C to the exhaust downstream side.

Fig. 3 and 4 are diagrams showing the flow of the exhaust gas in the mixing chamber 23. As shown in fig. 3, since the width of the flow path is narrowed from the 1 st chamber 23A to the 2 nd chamber 23B, and the side wall of one side (left side in the drawing) is bent and recessed, the exhaust gas flowing from the 1 st chamber 23A into the 2 nd chamber 23B generates a swirling flow.

As shown in fig. 4, the exhaust gas that has become a swirling flow flows into the connection pipe 24 through the outside of the rectifying member 50, or flows into the connection pipe 24 through the small hole 50C and the rectifying member 50. In the connection pipe 24, the exhaust gas flows downstream while swirling around the axial center of the connection pipe 24.

Here, the urea solution injection valve 30 injects the urea solution into the flow regulating member 50. The urea water to be injected (sprayed) is expanded in diameter from the upstream side to the downstream side by the flow regulating member 50, and the exhaust gas flowing in from the orifice 50C is guided to the exhaust downstream side by the claws 50D and diffused. The diffused urea water is mixed with the exhaust gas that has become a swirling flow in the connection pipe 24.

This makes it possible to diffuse the urea aqueous solution injected (sprayed) into the connecting pipe 24 and mix the urea aqueous solution with the exhaust gas that has become a swirling flow, and thus prevent the urea aqueous solution from adhering to the 2 nd chamber 23B or the wall surface of the connecting pipe 24 due to the flow of the exhaust gas. Therefore, the hydrolysis efficiency of the urea water can be improved.

Here, when the urea water adheres to the wall surface, the urea water is hydrolyzed by the exhaust gas or the heat of the wall surface, but the diffusion of ammonia in the connection pipe 24 is reduced. In contrast, in the rectifying unit 51 of the present embodiment, since the urea water can be prevented from adhering to the 2 nd chamber 23B or the wall surface of the connection pipe 24, the exhaust gas in the swirling flow in which the ammonia is uniformly diffused can be supplied to the SCR catalyst 41, and the exhaust gas purification ability of the SCR catalyst 41 can be improved.

Fig. 5 is a sectional view showing a rectifying unit 151 according to another embodiment. The same components as those in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted. As shown in fig. 5, the rectifying unit 151 includes: a rectifying member 50; and an impingement plate mixer 152 disposed on the exhaust gas downstream side of the flow rectification member 50. The impingement plate mixer 152 is provided with a mesh (not shown) and a diffusion plate 152A on an annular frame. The impingement plate mixer 152 is disposed facing the opening 50B in the vicinity of the downstream end of the flow rectification member 50.

In the rectifying portion 151 configured as described above, the urea water injected from the urea water injection valve 30 and diffused by the rectifying member 50 impinges on the wire mesh of the impingement plate mixer 152. This promotes hydrolysis of the urea water. The urea solution and the ammonia generated by the hydrolysis are further diffused by the diffusion plate 152A and flow into the connection pipe 24.

Therefore, the hydrolysis efficiency of the urea water can be further improved as compared with the exhaust gas purification unit including the rectifying portion 51, and the exhaust gas purification capability of the SCR catalyst 41 can be further improved.

Fig. 6 is a sectional view showing a rectifying portion 251 according to another embodiment. The same components as those in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted. As shown in fig. 6, the rectifying portion 251 includes: a rectifying member 50; and a hydrolysis catalyst 252 disposed on the exhaust gas downstream side of the flow rectification member 50. As the hydrolysis catalyst 252, for example, a hydrolysis catalyst in which titanium oxide is supported on the wall surface of a silicon nitride honeycomb or a metal honeycomb, or a hydrolysis catalyst in which alumina is supported on the wall surface of a cordierite honeycomb, or the like can be used. The hydrolysis catalyst 252 is disposed facing the opening 50B in the vicinity of the downstream end of the flow rectification member 50.

In the rectifying portion 251 configured as described above, the urea water injected from the urea water injection valve 30 and diffused by the rectifying member 50 passes through the hydrolysis catalyst 252. At this time, hydrolysis of the urea water is promoted. The urea water and the ammonia generated by the hydrolysis are transported to the exhaust downstream side of the connection pipe 24 by the exhaust gas that has become a swirling flow.

Fig. 7 is a sectional view showing a rectifying portion 351 according to another embodiment. The same components as those in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted. As shown in fig. 7, a rectifying member 350 is provided in the rectifying portion 351. The flow straightening member 350 is a pipe member of a truncated cone shape having both ends open, and is disposed coaxially with the urea solution injection valve 30.

The small-diameter opening 350A of the rectifying member 350 is disposed to face the injection port of the urea solution injection valve 30, and the large-diameter opening 350B of the rectifying member 350 is disposed to face the upstream end of the connection pipe 24. A gap through which the exhaust gas passes is left between the edge of the opening 350B of the flow-adjusting member 350, the upstream end of the connecting pipe 24, and the 2 nd chamber 23B.

The flow straightening member 350 is a porous member formed by molding a metal honeycomb into a truncated cone shape, and rectangular small holes 350C are formed at narrow intervals in the circumferential direction and the axial direction. Here, the partition walls 350D of the metal honeycomb are arranged to be inclined with respect to the thickness direction of the metal honeycomb and to be parallel to the axial center of the flow rectification member 350. Thus, the partition wall 350D functions as a guide portion for guiding the exhaust gas passing through the small hole 350C to the exhaust downstream side.

In the rectifying portion 351 configured as described above, the urea water injected (sprayed) expands in diameter from the upstream side to the downstream side by the rectifying member 350, and the exhaust gas flowing in from the small hole 350C is guided by the partition wall 350D to the exhaust downstream side, and is diffused, as in the rectifying portion 51 described above. The diffused urea solution is mixed with the exhaust gas that has become a swirling flow in the connection pipe 24.

Fig. 8 is a sectional view showing a rectifying unit 451 according to another embodiment. The same components as those in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted. As shown in fig. 8, the rectifying portion 451 includes: a rectifying member 350; and a hydrolysis catalyst 252 disposed on the exhaust gas downstream side of the flow rectification member 350.

In the rectifying portion 451 configured as described above, the urea water injected from the urea water injection valve 30 and diffused by the rectifying member 350 passes through the hydrolysis catalyst 252, as in the rectifying portion 251 described above. At this time, hydrolysis of the urea water is promoted. The urea water and the ammonia generated by the hydrolysis are transported to the exhaust downstream side of the connection pipe 24 by the exhaust gas that has become a swirling flow.

Fig. 9 is a sectional view showing the interior of the mixing chamber 23 and the connecting pipe 24 according to another embodiment. The same components as those in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted. As shown in fig. 9, the 1 st pipe 24A of the connection pipe 24 of the present embodiment has a double-pipe structure, and includes: a cylindrical outer tube 24C extending linearly from the exhaust upstream end to the exhaust downstream end of the 1 st pipe 24A; and a cylindrical inner pipe 24D linearly extending from the exhaust upstream end of the 1 st pipe 24A to the exhaust downstream side. The inner tube 24D is provided on the downstream side of the flow rectification member 50. In the present embodiment, the exhaust upstream end of the inner pipe 24D and the exhaust downstream end of the flow rectification member 50 have the same diameter, and are joined together. Thereby, the exhaust gas flowing outside the flow straightening member 50 flows to the exhaust downstream side through between the outer pipe 24C and the inner pipe 24D.

No opening is provided in a portion of the inner tube 24D on the exhaust upstream side, and the exhaust gas does not enter and exit between the inside and outside of the inner tube 24D in this portion. On the other hand, a plurality of small holes 24E are formed at narrow intervals in the circumferential direction and the axial direction in a portion on the exhaust downstream side of the inner pipe 24D, and exhaust gas flows in and out between the inside and the outside of the inner pipe 24D.

Fig. 10 is a diagram showing the flow of the exhaust gas in the mixing chamber 23 and the connection pipe 24. As shown in the figure, the exhaust gas that has become a swirling flow passes through the outside of the rectifying member 50 and flows between the outer pipe 24C and the inner pipe 24D of the connection pipe 24, or passes through the small hole 50C and the rectifying member 50 and flows into the connection pipe 24. In the connection pipe 24, the exhaust gas flows downstream while swirling around the axial center of the connection pipe 24. The exhaust gas flowing between the outer pipe 24C and the inner pipe 24D flows into the inner pipe 24D through the small holes 24E on the exhaust downstream side in the double-pipe structured portion.

The urea solution injection valve 30 injects the urea solution into the flow regulating member 50. The urea water to be injected (sprayed) is expanded in diameter from the upstream side to the downstream side by the flow regulating member 50, and the exhaust gas flowing from the orifice 50C is guided by the claws 50D to the exhaust downstream side, and is diffused. The diffused urea solution is mixed with the exhaust gas that has become a swirling flow in the connection pipe 24. This makes it possible to diffuse the urea aqueous solution injected (sprayed) into the connection pipe 24 and mix the urea aqueous solution with the exhaust gas that has become a swirling flow.

Here, in the connection pipe 24, the exhaust gas flows between the outer pipe 24C and the inner pipe 24D, thereby heating the exhaust gas flowing in the inner pipe 24D. This can suppress a decrease in the temperature of the exhaust gas due to latent heat when the urea aqueous solution is hydrolyzed, and can improve the conversion efficiency from the urea aqueous solution to ammonia, thereby improving the NOx purification rate in the SCR catalyst 41.

Further, since the urea water can be prevented from adhering to the wall surface of the 2 nd chamber 23A or the connection pipe 24 due to the flow of the exhaust gas, the hydrolysis efficiency of the urea water can be improved, and the diffusibility of ammonia in the connection pipe 24 can be improved.

Further, on the exhaust downstream side of the double tube structure portion, the exhaust gas flowing between the outer tube 24C and the inner tube 24D flows into the inner tube 24D and is mixed with the exhaust gas in which ammonia or urea water is diffused, whereby the diffusibility of ammonia in the exhaust gas can be further improved.

In the above embodiment, an example in which the inner pipe 24D of the 1 st pipe 24A having a double pipe structure is provided on the downstream side of the flow straightening member 50 has been described. Similarly, the inner tube 24D of the 1 st pipe 24A having a double-tube structure may be provided on the downstream side of the flow straightening member 350.

The present disclosure is not limited to the above-described embodiments, and can be implemented by being appropriately modified within a range not departing from the gist of the present disclosure.

The present application is based on Japanese patent application (Japanese application 2015-068050) applied on 30/03/2015 and Japanese patent application (Japanese application 2015-085716) applied on 20/04/2015, and the contents thereof are incorporated herein by reference.

Industrial applicability

The exhaust gas purification unit according to the present disclosure is useful in that the efficiency of hydrolysis of urea water is improved, and the diffusibility of ammonia in the exhaust gas is improved, thereby improving the exhaust gas purification ability of the catalyst.

Description of the reference numerals

1 exhaust gas purification unit, 20 front stage casing, 20A 1 st casing, 20B 2 nd casing, 21 st oxidation catalyst, 22 filter, 23 mixing chamber, 23A 1 st chamber, 23B 2 nd chamber, 24 connection piping, 24A 1 st piping, 24B 2 nd piping, 24C outer pipe, 24D inner pipe, 24E orifice, 30 urea water injection valve, 40 rear stage casing, 41 SCR catalyst, 42 nd 2 oxidation catalyst, 50 rectification member, 50A opening, 50B opening, 50C orifice, 50D claw, 51 rectification part, 151 rectification part, 152 impingement plate mixer, 152A diffusion plate, 251 rectification part, 252 hydrolysis catalyst, 350 rectification member, 350A opening, 350B opening, 350C orifice, 350D partition wall, 351 rectification part, 451 rectification part

Claims

1. An exhaust gas purification unit comprising:

a selective reduction catalyst that is provided in an exhaust system of an internal combustion engine and selectively reduces nitrogen oxides in exhaust gas using ammonia as a reducing agent,

an exhaust pipe for transporting an exhaust gas to the selective reduction catalyst,

a urea solution injection device that is disposed so as to face an exhaust upstream end of the exhaust pipe and injects urea solution into the exhaust pipe,

a chamber which connects an exhaust downstream end of a casing containing a catalyst and an exhaust upstream end of the exhaust pipe and forms a flow path for returning exhaust gas from the casing to the exhaust pipe, and

a flow regulating member provided in the chamber, the flow regulating member being a pipe member having a truncated cone shape extending from the vicinity of the injection port of the urea solution injection device toward the exhaust pipe while gradually expanding the diameter of the pipe member in diameter, the flow regulating member having a plurality of vent holes formed in the circumferential direction and the axial direction, each of the plurality of vent holes being provided with a guide portion for guiding the exhaust gas to the exhaust downstream side,

the chamber has: a 1 st chamber arranged at an exhaust downstream end of the casing and having an arc-shaped side surface; and a 2 nd chamber extending from a side surface of the 1 st chamber and connected to the exhaust pipe, the side surface being arc-shaped,

the width of the flow path narrows from the 1 st chamber to the 2 nd chamber,

the guide portion is bent toward the inner side of the flow regulating member with the upstream side of the air vent as a starting point,

a part of the large-diameter opening of the rectifying member is inserted into the exhaust upstream end of the exhaust pipe, and a gap through which exhaust gas passes is provided between an outer peripheral surface of an edge portion of the large-diameter opening of the rectifying member and an inner peripheral surface of the upstream end of the exhaust pipe.

2. The exhaust gas purifying unit according to claim 1,

includes a porous material disposed at an exhaust downstream end of the flow rectification member.

3. The exhaust gas purifying unit according to claim 1,

the exhaust gas treatment device includes a hydrolysis catalyst disposed at an exhaust gas downstream end of the rectifying member.

4. The exhaust gas purifying unit according to any one of claims 1 to 3,

the exhaust pipe includes an inner pipe through which the urea solution is injected from the urea solution injection device, and an outer pipe having a double pipe structure together with the inner pipe, and a flow path for exhaust gas is formed inside the inner pipe and between the inner pipe and the outer pipe.

5. An exhaust gas purification unit comprising:

a urea solution injection device for injecting urea solution into the exhaust pipe,

a chamber connecting an exhaust downstream end of the catalyst-containing case and an exhaust upstream end of the exhaust pipe, and

a flow regulating member connected to the exhaust pipe, having a plurality of vent holes formed in a circumferential direction and an axial direction, and having a guide portion for guiding the exhaust gas to an exhaust downstream side; wherein the content of the first and second substances,

the exhaust pipe includes an inner pipe through which the urea solution is injected from the urea solution injection device, and an outer pipe having a double pipe structure together with the inner pipe, and a flow path for exhaust gas is formed inside the inner pipe and between the inner pipe and the outer pipe;

the flow regulating member is connected to the exhaust upstream end of the inner pipe, and is formed in a truncated conical shape so as to extend from the vicinity of the injection port of the urea solution injection device to the exhaust upstream end of the inner pipe while gradually expanding in diameter,

the width of the flow path narrows from the 1 st chamber to the 2 nd chamber,

the large-diameter opening of the flow straightening member is arranged to face the upstream end of the inner pipe, and a gap through which exhaust gas passes is provided between an edge of the large-diameter opening of the flow straightening member, the upstream end of the inner pipe, and the 2 nd chamber.

6. The exhaust gas purifying unit according to claim 5,

a vent hole is formed in a predetermined range on the exhaust downstream side of the inner pipe.